1. Field of the Invention
This invention relates to a projecting device.
2. Description of the Prior Art
There is already known the use of a so-called compound lens system, composed of a plurality of optical systems, each capable of projecting a partial area or a pixel (picture element) of the object onto a determined partial area of the image plane (such system being hereinafter referred to as a plural element lens system) arranged in a plane perpendicular to the optical axis and along a determined direction, for example, along the slit employed in a copier utilizing the slit-exposure process for the purpose of reducing the conjugate distance from the object plane to the image plane and thus rendering the entire apparatus of the copier more compact.
Such an element lens system is already disclosed, for example in the U.S. Pat. No. 3,592,542 as a system composed of three axially arranged lenses, or in U.S. Pat. No. 3,584,952 as a system composed of three axially arranged lenses (in these systems the central lens functioning as a field lens), or in Japanese Patent Laid-Open Sho 53-122426 corresponding to the U.S. patent application Ser. No. 889,404, now abandoned, as a system composed of two bar lenses having axial lengths larger than the effective aperture and in which the central air layer functions as an air field lens. Although these known lenses are advantageous in effectively transmitting the light to the image plane by the function of said field lens, they are still defective in that they require delicate optical adjustment for the eventual eccentricity of two or three lenses arranged in the axial direction and the dust present in the vicinity of the field lens is projected on the final image plane to form a noise in the obtained image.
In U.S. Pat. No. 3,580,675 there is disclosed an element lens system composed of a single oblong lens which does not form an intermediate image in the scanning direction in a plane perpendicular to the optical axis but does form an intermediate image in the array direction orthogonal to said scanning direction, thus forming a final image erect only in one direction. The element lens system of the present invention is, however, different in that it forms an intermediate image both in the scanning direction and in the array direction in a plane perpendicular to the optical axis, thus forming a final image erect in both directions.
The element lens system of the present invention is also different from that obtainable from the combination of U.S. Pat. Nos. 3,580,675 and 3,592,542 in the manner explained in the following.
The element lens system disclosed in U.S. Pat. No. 3,592,542 shows, as represented in FIG. 6 thereof, a substantially rectangular light intensity distribution practically without the effect of the eclipse of aperture, except for the effect of the cosine the 4th-power rule, because of the presence of a complete field lens. Stated differently, the obtained light intensity distribution is substantially represented by a determined bias amount overlapped with the effect of the cosine to the 4th-power rule, etc. In the case of arranging a plural number of such element lens systems in a row with a given pitch and further arranging a plural number of such rows in a staggered fashion mutually displaced by a half pitch, a very accurate arrangement of the pitch, with very difficult adjustment is required, in order to obtain a uniform exposure integrated in time, in the scanning direction.
In addition to the aforementioned transmission-type optical systems, there is also known a reflection-type element lens system composed of a single bar lens as disclosed in Japanese Patent Laid-Open Sho 54-54057 corresponding to U.S. patent application Ser. No. 949,047 now abandoned. Such an element lens system, however, requires a difficult optical adjustment between the bar lens and the associated mirror.